These discussions and examples are very helpful to be, as a beginner. I did April 30 puzzle four times, so I missed yesterday. The first three crashed. Finally, I did a forced chain thing and broke it open. In each case I thought I was being very logical, until I reached the point of conflict.
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Haven't done today's yet, but with all the help that has been posted, it should be fun. I think there is one aspect to Swordfish that doesn't seem to be mentioned clearly: It has direction. When you identify the three columns (primary) and the three rows (secondary), the numbers to eliminate must be on those three (secondary) rows, right? So if you do it the other direction, you set up three rows (primary) that meet three columns (secondary), and the numbers eliminated are on those (secondary) columns. I think that explains a few questions I have seen about "why didn't this one get included -- or excluded."
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Now, here's a suggestion. I print out the puzzles, because I do them in my easy chair at the end of the day, not at the computer. I find all of the "easy" numbers using basic logic. Then I put in all of the possibilities for the remaining cells. This bit of work takes me about 15 to 20 minutes by hand. I do it in ink, and then put in the numbers in red Sharpie, so things don't get confused. Anyway, it would be a big time saver if each puzzle could be printed out from the beginning with all of the possibilities shown in each cell. Then we can just mark them out as we go. It would save a lot of time. Is this already possible and I just haven't found out how to do it? Many thanks.

We do sudoku for fun - I hope, so I don't want to do it the way a computer does it. A friend of mine suggested that the proper way to do a problem is in ink - no erasing!! ok OK this is too tough - remembering that these two cells are 39 and those other three are 568 etc.. is difficult. BUT I have an easy way of noting my route to a solution, and the logic used at each stage so on a difficult problem that I have solved, I have sometimes started again, using the recorded crib for method, but doing it in "ink". It can usually be done, and certainly I have seldom found the need to fill in a cell with more than 3 candidate numbers.

So puzzles that are graded easy and medium, are more fun if done in "ink".Mind you that brings us to puzzles that are graded easy and not so easily done even with pencil and erasing!- but that's another matter!